1. Technical Field
The present invention relates to transflective liquid crystal display panels and electronic apparatuses equipped with transflective liquid crystal display panels. In particular, the invention relates to a transflective liquid crystal display panel of a so-called fringe-field-switching (FFS) mode having a high aperture and reduced light leakage, and to an electronic apparatus equipped with such a transflective liquid crystal display panel.
2. Related Art
The development of transflective liquid crystal display panels having both transmissive and reflective properties has been advancing considerably over the recent years. A transflective liquid crystal display panel generally has a plurality of pixel regions, each having a transmissive section equipped with a pixel electrode and a reflective section equipped with both a pixel electrode and a reflecting plate. When in a dark environment, a transflective liquid crystal display panel is configured to turn on a backlight and utilize the transmissive sections to display an image. On the other hand, in a lighted environment, a transflective liquid crystal display panel does not turn on the backlight but instead utilizes external light by using the reflective sections to display an image.
The majority of liquid crystal display panels of related art are of a so-called vertical electric field mode in which a pair of substrates are each provided with electrodes, such as a twisted nematic (TN) type or a vertical alignment (VA) type, but a so-called transverse electric field mode in which electrodes are provided in only one of a pair of substrates, such as an FFS type, is also known. Examples of an FFS-mode liquid crystal display panel are disclosed in JP-A-2002-14363 and JP-A-2002-244158. An FFS-mode liquid crystal display panel is capable of achieving bright display due to having a wide viewing angle, high contrast, and high aperture.
Regarding FFS-mode liquid crystal display panels, a transflective type has been developed over the recent years, examples of which being disclosed in JP-A-2003-344837 and JP-A-2006-337625. An FFS-mode transflective liquid crystal display panel of related art will be described with reference to FIGS. 7 and 8. It should be noted that the layers and components in the drawings attached to this specification are shown with different scales from the original scales such that they are shown with dimensions recognizable to the viewer. This means that the layers and components in the drawings are not necessarily shown in proportion to their actual dimensions.
FIG. 7 is a plan view illustrating one of a plurality of pixels included in an FFS-mode transflective liquid crystal display panel of related art. FIG. 8 is a schematic cross-sectional view taken along line VIII-VIII in FIG. 7.
An FFS-mode transflective liquid crystal display panel 50 includes an array substrate AR and a color filter substrate CF. The array substrate AR includes a first transparent substrate 51, a plurality of scanning lines 52 and common wire lines 53 arranged parallel to each other on the first transparent substrate 51, and a plurality of signal lines 54 arranged crosswise to the scanning lines 52 and the common wire lines 53 on the first transparent substrate 51. The scanning lines 52 and the common wire lines 53 have their surfaces covered with a gate insulating film 55, whereas the signal lines 54 are disposed on the gate insulating film 55. The gate insulating film 55 has semiconductor layers 56 disposed thereon in areas corresponding to gate electrodes G of the scanning lines 52. A source electrode S and a drain electrode D extending from each of the signal lines 54 are partially stacked on each semiconductor layer 56. The gate electrode G, the source electrode S, and the drain electrode D in each pixel region constitute a thin film transistor (TFT). The entire surface of the first transparent substrate 51 is covered with a protective insulating film 57.
The protective insulating film 57 is covered with an interlayer film 58. In the reflective section RA of each pixel region, the interlayer film 58 has an uneven surface (not shown). In contrast, in other areas of the pixel region, the interlayer film 58 has a flat surface. In the reflective section RA of each pixel region, the interlayer film 58 has disposed thereon a reflecting plate 60 composed of aluminum or an aluminum alloy. Furthermore, the reflecting plate 60 and the interlayer film 58 in each pixel region have disposed thereon a lower electrode 61 composed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The lower electrode 61 is electrically connected to the corresponding common wire line 53 via a contact hole 62 formed in the protective insulating film 57 and gate insulating film 55 disposed on the common wire line 53. In each pixel region, the interlayer film 58 and the protective insulating film 57 have a contact hole 63 at a position corresponding to the drain electrode D, such that the drain electrode D is exposed through the contact hole 63. Of the total area occupied by the lower electrode 61 in each pixel region, the area occupied by the reflecting plate 60 defines the reflective section RA and the area not occupied by the reflecting plate 60 defines the transmissive section TA.
Each lower electrode 61 and the interlayer film 58 are covered with a capacitor insulating film 64 composed of, for example, silicon nitride or silicon oxide. The capacitor insulating film 64 covers the wall surface of each contact hole 63 in such a manner that the corresponding drain electrode D is exposed through the contact hole 63. In each pixel region, the capacitor insulating film 64 has disposed thereon an upper electrode 66 composed of a transparent conductive material such as ITO or IZO and having a plurality of parallel slits 65. The opposite ends of each slit 65 in the upper electrode 66 are closed ends. The upper electrode 66 is electrically connected to the drain electrode D via the contact hole 63. The upper electrode 66 and the slits 65 thereof are covered with an alignment film (not shown).
On the other hand, the color filter substrate CF includes a second transparent substrate 67 on which a black matrix 68, color filter layer segments 69, and an overcoating layer 70 are disposed. The overcoating layer 70 covers the black matrix 68 and the color filter layer segments 69, and moreover, the overcoating layer 70 has an alignment film (not shown) disposed thereon. The FFS-mode transflective liquid crystal display panel 50 is formed by disposing the array substrate AR and the color filter substrate CF opposite to each other in a manner such that the upper electrodes 66 of the array substrate AR and the color filter layer segments 69 of the color filter substrate CF face each other, and then sealing a liquid crystal layer 71 between the array substrate AR and the color filter substrate CF.
The transflective liquid crystal display panel 50 of the related art can perform display with an aperture higher than that in a vertical electric field mode. However, the liquid crystal display panels in recent years, particularly, compact liquid crystal display panels used in, for example, portable telephones, are becoming more and more highly defined. Therefore, a liquid crystal display panel having an even higher aperture and brightness is in great demand. In addition, in a transflective liquid crystal display panel like the one described above, a variation in color tone can sometimes occur between the display mode using the transmissive sections and the display mode using the reflective sections. For this reason, a liquid crystal display panel having reduced variation in display quality and allowing for a uniform display operation under either display mode is in demand.